1. Field of the Invention
The present invention relates to a hip prosthesis and more particularly to the femoral component of a hip prosthesis. The prosthesis of the present is the type that is cemented in position in the medullary canal of the femur. The hip of the present invention employs spacers to accurately position the prosthesis in the medullary canal to create a cement mantle of optimal thickness and to ensure neutral positioning of the prosthesis in the medullary canal. The prosthesis may also be provided with a collar that will optimally contact the calcar when implanted.
2. Prior Art
Total hip prosthesis have been in use for some time. These prosthesis generally comprise a femoral component which includes a stem or shaft, a neck and a spherical ball mounted on the neck. The ball is positioned into the second major component of the prosthesis which is an acetabular cup. The acetabular cup generally made from ultra high molecular weight polyethylene and includes a spherical opening to receive and contain the ball of the femoral component The normal movement of the leg is facilitated by the ball of the femur freely moving in the spherical cavity of the acetabular cup.
Some femoral components of hip prosthesis include a collar which is below the neck of the prosthesis and which is in contact with the bone in the femur. The particular configuration of the collar in prior art prosthesis has considerable variation.
U.S. Pat. No. 4,851,004, U.S. Pat. No. 4,068,324 and DES. 280,020 disclose hip prosthesis with a collar or flange which is somewhat elliptical in shape and has a greatest width at the lateral portion of the collar.
U.S. Pat. No. 4,642,124, U.S. Pat. No. 4,516,277, U.S. Pat. No. 4,514,865 and DES. 254,987 disclose collars which are essentially round
U.S. Pat. Nos. 4,795,472 and 4,871,369 disclose hip prosthesis that have a collar that extends medially from the stem.